The Biogeochemistry Core will support geochemical and microbiological measurements on behalf of earth science and environmental engineering Projects 5, 6, and 7 and groundwater analyses for constituents of potential health concern for biomedical Projects 3 and 4. Using a VG Axiom (magnetic sector) High- Resolution Inductively Coupled Plasma-Mass Spectrometer (HR ICP-MS) housed at Lamont-Doherty Observatory, approximately 10,000 samples of groundwater and sediment digests will be analyzed for up to 33 major and trace elements. Existing methods will be refined to determine As concentrations and speciation in the field and in the laboratory. Sediment deposition rates will be determined over a range of time scales using the radioisotopes 14C, 137Cs, and 210Pb. Through collaboration with Dartmouth College and the Universite Paul Cezanne (France), the Biogeochemistry Core will support the spectroscopic characterization of Fe and As mineralogy and speciation for selected sediment samples at various synchrotron facilities. This will include bulk analysis by X-ray Absorption Near-Edge Structure (XANES) and Extended X-ray Absorption Fine-Structure (EXAFS) spectroscopy, as well microbeam X-ray microprobe analysis to determine spatial heterogeneity. The Biogeochemistry Core will also support a concerted effort to identify the microorganisms responsible for mobilizing As in groundwater. This work will be conducted on the Columbia Health Sciences campus and in collaboration with Duquesne University. Using both culture-based on non-culture-based methods, the presence of arsenic-metabolizing bacteria will be determined in selected aquifer material from the U.S. and Bangladesh. The microbial diversity of groundwater and sediment samples will be established using 16srRNA and specific genes, such as the Arr and Ars operon. DMA and RNA Stable Isotope-Probing methods will also be developed.